Amniotic fluid chromosome analysis is performed to detect numerical and structural abnormalities such as:
- Larger interstitial or terminal deletions and duplications
Reasons to perform amniotic fluid chromosome analysis include:
- Mother’s age 35 years or older at time of delivery
- Prior pregnancy or child with a chromosomal abnormality
- Abnormal ultrasound findings
- Multiple miscarriages
- Abnormal Triple, Quad or Penta screen
- High or low maternal serum alpha-fetoprotein screen
- Family history of chromosomal abnormality
- Mother of any age requesting prenatal testing
Testing for specific trisomies using fluorescence in situ hybridization (FISH) is commonly performed in conjunction with chromosome analysis. To order, please specify Trisomy screen by FISH and chromosome analysis on the Test Request Form.
In addition to cytogenetic studies, an amniotic fluid alpha-fetoprotein (AF-AFP) assay can also be performed to potentially detect neural tube defects or other developmental failures of body wall closure, such as gastroschisis.
Analysis is performed on cultured cells.
A minimum of 15 metaphases from 15 colonies are examined and 2 karyotypes are prepared.
- 20-30 ml unspun amniotic fluid in sterile, plastic, screw-top tubes
- Label specimen tube with patient’s name and a second identifier (ex: DOB, hospital ID)
- Maintain specimen at room temperature and transport to the Colorado Genetics Laboratory immediately
Samples must be accompanied by a completed Test Request Form including pertinent clinical and family history, and gestational age at the time of specimen collection.
Turn Around Time
Generally 7-12 days, depending on the viability of cells in the amniotic fluid sample.
Trisomy Screen by FISH for Trisomy 21, 18 and 13, and sex chromosome aneuploidies is performed within 24-48 hours for quick analysis of the most common prenatal genetic conditions.